A judge said Lorraine Thorpe had been brought up "with no real understanding of what is right and what is wrong".

She was convicted of taking part with Paul Clarke (41) in the murders of Desmond Thorpe and Rosalyn Hunt last August.

Ms Hunt (41) was beaten to death in Ipswich over several days, with Thorpe responsible for kicking, punching and stamping on her head.

Mr Thorpe (43) a "vulnerable" alcoholic, was smothered amid fears that he would tell the police about the first murder.

Thorpe, now 16, of Clapgate Lane, Ipswich, was told she must serve at least 14 years behind bars as she was sentenced at the Old Bailey.

Mr Justice Saunders said the teenager could be "manipulative" and was not acting entirely under Clarke's control, adding: "She found violence funny and entertaining."

Clarke, of Mountbatten Court, Ipswich, has already been jailed for life with a minimum term of 27 years.

Thorpe became Britain's youngest convicted female double murderer after the pair's trial at Ipswich Crown Court, which ended last month.

Mary Bell, detained at the age of 11 in 1968 for the manslaughter of two boys aged three and four, remains the youngest female killer. The youngest girl to be convicted of a single murder was Sharon Carr, who was just 12 when she killed trainee hairdresser Katie Rackliff in 1992.

The judge said Clarke was the "instigator" in the murder of Ms Hunt, also an alcoholic, although Thorpe "played a full part".

"She was responsible for protracted kicking, punching and stamping on Rosalyn.

"Far from being sorry, Lorraine appears to have gloried in it, describing to her friends at one stage how she stamped on Rosalyn's head."

Thorpe's father was a "hopeless alcoholic" and "very vulnerable person" unable to walk unaided or do anything for himself, and she was his carer.

Smothered

"He died by being smothered to death," said the judge. "The only possible explanation for his death can be the fear that he would go and tell the police what happened to Rosalyn Hunt."

Thorpe was influenced by Clarke, the "dominant" member of a group of heavy drinkers, and would try to impress him, said the judge.

He added: "I don't accept she was entirely under the control of Mr Clarke. She is someone who can be quite stubborn and wilful and is capable of being highly manipulative herself."

The judge said the case was "exceptional" and said of Thorpe: "Her story is an appalling one."

The court heard that Thorpe's parents split up when she was 12 and she initially lived with her mother before going to look after her father at 13. Father and daughter would move "from one squalid flat to another", sometimes even living in tents. "Social services were unable to keep track of her," said the judge.

All the evidence was that they "loved each other very much".

Through drinking they met Clarke and lived at his flat for a time.

Thorpe was growing up in "totally the wrong place and atmosphere to bring up a young girl", said the judge. "She has been left with no real understanding of what is right and what is wrong."